Circulating interleukin-6 levels in patients with bronchial asthma.

Circulating interleukin-6 (IL-6) levels were determined using a sensitive enzyme immunoassay in adults with asthma in stable condition during naturally occurring attacks and before and after allergen inhalation tests. IL-6 was significantly elevated even in asymptomatic asthmatic subjects (n = 17) compared with normal control subjects (n = 17). During naturally occurring asthmatic attacks, serum IL-6 levels were significantly elevated in comparison with those in a symptom-free condition (4 wk interval; n = 8, p < 0.01). No significant difference was observed in serum IL-6 levels obtained from control asymptomatic asthmatic subjects during the period (n = 10). There was a significant elevation in circulating IL-6 levels in eight asthmatic patients following inhalation of allergen but not methacholine. These results suggest that IL-6 is involved in the pathophysiology of bronchial asthma.